Pump with reciprocating high pressure seal and valve for vehicle braking systems

ABSTRACT

A pump apparatus includes a housing having a bore formed therethrough. A piston is disposed within the bore for reciprocal movement therein. The piston includes a piston body, and an inlet flange extending radially outwardly from the piston body. An outer peripheral surface of the inlet flange and a wall of the bore define a first passageway. A retaining flange extends radially outwardly from the piston body and have a substantially square transverse section. An outer peripheral surface of the retaining flange and the wall of the bore define a second passageway. An intermediate portion is disposed between the inlet flange and the retaining flange. An annular seal is disposed around the intermediate portion of the piston body. The seal slidingly engages the wall of the bore, and the seal and the piston cooperate to form a check valve assembly.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of application Ser. No. 10/678,676 filed Oct. 3, 2003.

BACKGROUND OF THE INVENTION

This invention relates in general to brake systems for vehicles and in particular to a pump assembly with a combination reciprocating high-pressure seal and fluid inlet check valve for use within brake systems.

In conventional vehicular brake systems having anti-lock brake, traction control and/or vehicle stability control, a supply of hydraulic fluid for the vehicle brakes is modulated by a hydraulic control unit. Various hydraulic pumps may be employed to selectively supply hydraulic fluid to the vehicle brakes. Several hydraulic pump designs are known.

U.S. Pat. No. 4,556,261 to Farr discloses a prior art pump and skid sensing assembly for a vehicle hydraulic anti-skid braking system, as shown in FIGS. 1 and 2. The assembly comprises a housing 1 incorporating a hydraulic pump 2, and a solenoid-operated valve assembly 3. Only the operation of the pump 2 will be described herein, as the operation of the rest of the anti-skid braking system is not relevant to the present invention. The pump 2 includes a plunger 10, which reciprocates within a stepped bore 11 in the housing 1. The plunger 10 is engageable with a drive mechanism comprising a ring 12 rotatable on a shaft 4. The plunger 10 carries an ‘O’ ring seal 18 and a lip seal 19. The seals 18 and 19 are disposed on opposite sides of a passage 20 leading to the valve 3. The seals 18 and 19, the plunger 10, and the bore 11 define a chamber 22. A reservoir 35 supplies the chamber 22 with fluid.

The seal 19, which is illustrated in detail in FIG. 2, comprises an annular ring of elastomeric material, which is received in an annular groove 25 in the plunger 10. The groove 25 is parallel sided and is of an axial length greater than the thickness of the seal 19. Opposite faces 26 and 27 of the seal 19 are respectively planar and of reduced area, with the face 27 of reduced area being provided with at least one diametrical slot 28 which communicates with one or more passages 29 in the inner peripheral edge of the seal 19. The planar face 26 is adapted to seal against the adjacent, inner, face of the groove 25 to prevent flow from the secondary chamber 22 into the reservoir 35. The seal 19 is rather complex in that it contains at least one slot 28 and at least one passage 29 formed therethrough to control fluid flow through the seal 19.

As the plunger 10 is moved towards the ring 12, the seal 19 moves relative to the plunger 10 so that the face 26 is spaced apart from the adjacent face of the groove 25. This allows fluid from the reservoir 35 to be drawn into the increasing volume of the chamber 22 past the seal 19 with flow taking place through the slot 28 and the at least one passage 29 in the seal 19. As the plunger 10 is moved in the opposite direction, the face 26 of the seal 19 seals against the adjacent face of the groove 25 so that fluid cannot flow between the plunger 10 and the seal 19 or through the slot 28 and the at least one passage 29 within the seal 19. The seal 19 in this condition thus provides a seal between the plunger 10 and the wall of the bore 11, allowing the plunger 10 to pump fluid from the secondary chamber 22 into the primary chamber 23.

SUMMARY OF THE INVENTION

The present application describes various embodiments of a pump apparatus. One embodiment of the pump apparatus includes a housing having a bore formed therethrough. A piston is disposed within the bore for reciprocal movement therein. The piston includes a piston body, and an inlet flange extending radially outwardly from the piston body. An outer peripheral surface of the inlet flange and a wall of the bore define a first passageway. A retaining flange extends radially outwardly from the piston body and have a substantially square transverse section. An outer peripheral surface of the retaining flange and the wall of the bore define a second passageway. An intermediate portion is disposed between the inlet flange and the retaining flange. An annular seal is disposed around the intermediate portion of the piston body. The seal slidingly engages the wall of the bore, and the seal and the piston cooperate to form a check valve assembly.

Other aspects of the pump apparatus will become apparent to those skilled in the art from the following detailed description, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a known prior art hydraulic pump assembly.

FIG. 2 is a cross sectional view of the seal of the known prior art hydraulic pump assembly illustrated in FIG. 1.

FIG. 3 is a perspective view of a first embodiment of a piston in accordance with the present invention.

FIG. 4 is a cross sectional view of the piston shown in FIG. 3, taken along line 4-4, with the piston disposed within a first embodiment of a pump assembly, in accordance with the present invention.

FIG. 5 is a cross sectional view of the pump assembly of FIG. 4.

FIG. 6 is an enlarged cross sectional view of a portion of a second embodiment of a pump assembly and a second embodiment of a piston in accordance with the present invention.

FIG. 7 is a cross sectional view of a portion of a third embodiment of a pump assembly having a third embodiment of a piston and showing the piston in one extreme of travel.

FIG. 8 is a cross sectional view of the third embodiment of the pump assembly illustrated in FIG. 7, showing the piston in another extreme of travel.

FIG. 9 is a perspective view of the piston illustrated in FIGS. 7 and 8.

FIG. 10 is a top plan view of the piston illustrated in FIG. 9.

FIG. 11 is a perspective view of a portion of a fourth embodiment of the piston illustrated in FIGS. 7 through 9.

FIG. 12 is a perspective view of a portion of a fifth embodiment of the piston illustrated in FIGS. 7 through 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring again to the drawings, there is illustrated in FIG. 3, a first embodiment of a piston, indicated generally at 50, in accordance with this invention. The piston 50 comprises a shaft 51, a retaining flange 52, and an inlet flange 53. The retaining flange 52 extends substantially perpendicular from the shaft 51 at a first end portion 54 of the shaft 51. The inlet flange 53 extends substantially perpendicular from the shaft 51 below and spaced apart from the retaining flange 52. The retaining flange 52 and the inlet flange 53 cooperate to define an intermediate portion 55 of the shaft 51 disposed between retaining flange 52 and the inlet flange 53.

The shaft 51 is generally elongated along a longitudinal axis A. The shaft 51 includes a second end portion 56, opposite the first end portion 54. The intermediate portion 55, described above is disposed between the first end portion 54 and the second end portion 56. The second end portion 56 is engaged by a driving mechanism (not shown) for reciprocatingly driving the piston 50. The intermediate portion 55 of the shaft 51 may have a generally circular cross section. The intermediate portion 55 extends outwardly from the axis A to a radius R₁, as is shown in FIGS. 4 and 5, and as will be described further below. The intermediate portion 55 has at least one passageway 57 formed therethrough. In a preferred embodiment, the at least one passageway 57 comprises a plurality of longitudinally extending grooves, with preferably semi-circular cross-section, that have been machined through the intermediate portion 55 of the shaft 51 around the periphery of the intermediate portion 55. In a more preferred embodiment, the at least one passageway 57 comprises a plurality of longitudinally extending notches molded in the intermediate portion 55, with preferably rectangular or diamond-shaped cross-section. However, it will be appreciated that the at least one passageway 57 may be formed in the intermediate portion 55 in any manner, and may have any suitable cross-section. As used throughout the application, semi-circular encompasses any portion of a circle, which includes but is not limited to half of a circle. The at least one passageway 57 is formed through the intermediate portion 55 such that no part of the at least one passageway 57 extends further into the intermediate portion 55 than a radius R₂ from the axis A.

The retaining flange 52 may have a generally circular cross section, and has a radius taken from the axis A that is larger than the radius R₁ of the intermediate portion 55, the purpose of which will be described below. The retaining flange 52 has at least one passageway 58 formed therethrough. In a preferred embodiment, the at least one passageway 58 comprises a plurality of longitudinally extending grooves, preferably with semi-circular cross-section, that have been machined through the retaining flange 52 around the periphery of the retaining flange 52. In a more preferred embodiment, the at least one passageway 58 comprises a plurality of longitudinally extending notches molded in the retaining flange 52, with preferably rectangular or diamond-shaped cross-section. However, it will be appreciated that the at least one passageway 58 may be formed in the retaining flange 52 in any manner, and may have any suitable cross-section. It will also be appreciated that the retaining flange 52 may be any one of a plurality of nubs or tangs extending outwardly from said piston 50, the purpose of which will be described below. The at least one passageway 58 is formed through the retaining flange 52 such that the at least one passageway 58 does not extend into the retaining flange 52 any closer than a radius R₃ from the axis A as seen in FIG. 4. The radius R₃ is smaller than the radius R₁ of the intermediate portion, such that the at least one passageway 58 is aligned to radially overlap the at least one passageway 57, and the at least one passageway 58 and the at least one passageway 57 are connected in fluid communication.

The inlet flange 53 may have a circular cross section, and has at least one passageway 59 formed therethrough. In a preferred embodiment, the at least one passageway 59 comprises a plurality of longitudinally extending grooves, preferably with semi-circular cross-section, that have been machined through the inlet flange 53 around the periphery of the inlet flange 53. In a more preferred embodiment, the at least one passageway 59 comprises a plurality of longitudinally extending notches molded in the inlet flange 53, with preferably rectangular or diamond-shaped cross-section. However, it will be appreciated that the at least one passageway 59 may be formed in the inlet flange 53 in any manner, and may have any suitable cross-section. The at least one passageway 59 is formed through the inlet flange 53 such that the at least one passageway 59 does not extend further into the inlet flange 53 any closer than a radius R₄ from the axis A, as seen in FIG. 4. The radius R₄ is greater than the radius R₁, the outer radius of the at least one passageway 57, such that even though the at least one passageway 57 and the passageway 59 may be aligned to overlap radially, the at least one passageway 57 and the at least one passageway 59 are not directly communicably connected with one another.

The piston 50 is suitable for use in a pump assembly, such as the first embodiment of a pump assembly, indicated generally at 60, in FIGS. 4 and 5. The pump assembly 60 comprises a housing 61 having a bore 62 formed therethrough. The piston 50 is mounted for reciprocal movement within the bore 62 of the housing 61. Preferably, the piston 50 is formed of a material that is sufficient to sustain operation of the pump assembly 60 under operating conditions within the pump assembly 60 as described herein, such as the relatively high operating pressures of a pump assembly within a vehicle brake system. Additionally, in a preferred embodiment, the piston 50 is comprised of materials that are compatible with hydraulic brake fluid.

An annular high-pressure seal 63 is disposed around the intermediate portion 55 of the piston 50. In a preferred embodiment, the high-pressure seal 63 has a generally rectangular radial cross section as illustrated for each portion of the seal 63 shown on either side of the axis A in FIG. 4. However, it will be appreciated that the seal may have any radial cross-section. In a preferred embodiment, the seal 63 is not as thick as the intermediate portion 55 is long, such that the seal 63 can reciprocate between the retaining flange 52 and the inlet flange 53 of the piston 50, as will be described below. The seal 63 is preferably elastomeric. In a preferred embodiment, the seal 63 includes a base material, such as Polytetrafluoroethylene (PTFE) sold under the trade name Teflon® and manufactured by DuPont, and a filler material, such as carbon. In a more preferred embodiment, the seal 63 includes carbon fiber, or other high tensile strength fibers suitable for use in composite materials. Preferably, the seal 63 is formed of a material that is sufficient to sustain operation of the pump assembly 60 under operating conditions within the pump assembly 60 as described herein, such as the relatively high operating pressures of a pump assembly within a vehicle brake system. In a preferred embodiment, the seal 63 is formed of a material that is sufficient to sustain operation of the pump assembly 60 with an operating pressure range of about 0 to about 250 bars absolute pressure within the pump assembly 60, as will be described in more detail below. However, it will be appreciated that operating pressure within the pump assembly 60 may vary, and may be a negative pressure under some operating conditions, as will be described below. In a preferred embodiment, the seal 63 is formed of a material that is sufficient to sustain operation of the pump assembly 60 in a temperature range of about −40 degrees Celsius to about 120 degrees Celsius. Additionally, in a preferred embodiment, the seal 63 is comprised of materials that are compatible with hydraulic brake fluid.

The seal 63 has a first surface 64 that slidingly engages the walls of the housing 61 that form the bore 62 to form a dynamic seal therebetween. The seal 63 also has a second surface 65 that slidingly engages the outer periphery of the intermediate portion 55 of the piston 50, although such is not required. The seal 63 is able to move relative to the intermediate portion 55 between a first position, in which the seal 63 contacts the retaining flange 52 and a second position, in which the seal 63 contacts the inlet flange 53 as will be described below. The second surface 65 may seal against only the outer periphery of the intermediate portion 55, and does not contact the inner periphery of the at least one passageway 57, such that the seal 63 does not enter the at least one passageway 57. Thus, no seal is formed between the seal 63 and the intermediate portion 55.

The seal 63 further includes a third surface 66 that engages a surface 68 of the retaining flange 52 when the seal 63 is in the first position thereof. As indicated above, in a preferred embodiment, the at least one passageway 58 is a plurality of similar passageways in the form of grooves that are symmetrically positioned around the retaining flange 52, so that the seal 63 is evenly axially supported by the retaining flange 52 when seated in the first position.

The seal 63 has a fourth surface 67 that may engage a sealing surface 69 of the inlet flange 53 when the seal 63 is in a second position relative to the inlet flange 53, as will be described below. When the seal 63 is in the second position, the fourth surface 67 engages the sealing surface 69. The seal 63 prevents fluid flow through the at least one passageway 59 through the inlet flange 53, because, as is best shown in FIG. 5, the seal 63 seats against the sealing surface 69 blocking the passageway 59. Fluid is not able to flow out of the at least one passageway 57 past the seal 63, so fluid is not able to flow from the at least one passageway 57, around the seal 63, and into the at least one passageway 59. Therefore, the seal 63, in the second position, prevents the at least one passageway 57 and the at least one passageway 59 from fluid communication with one another.

Thus, the seal 63 and the inlet flange 53 cooperate to form a first check valve assembly 70, as will be described in more detail below. In a preferred embodiment, the at least one passageway 59 is a plurality of similar passageways that are symmetrically positioned around the inlet flange 53, so that the seal 63 is evenly supported by the inlet flange 53 when seated in the second position.

The pump assembly 60 will now be further described. The second end portion 56 of the piston 50 is mounted so that the piston 50 may reciprocate within the bore 62 of the housing 61. The piston 50 slides against the walls of the bore 62 as the piston 50 reciprocates. A seal 71 may be provided or formed by the piston 50 and the walls of the bore 62. The seal 71, the seal 63, and the piston 50 define an inlet chamber 72 within the bore 62. A fluid inlet 73 is communicably connected to the inlet chamber 72 to supply fluid to the pump assembly 60, as will be described below. Alternatively, it will be appreciated that the seal 71 may not be provided, and the inlet chamber 72 may extend such that the fluid of the inlet chamber 72 may be used to lubricate the piston 50 and the walls of the bore 62 to facilitate the reciprocal movement therebetween. In a more preferred embodiment, an o-ring (not shown) may be disposed around the shaft 51 of the piston 50 near the second end portion 56 of the piston 50 instead of the seal 71 such that the inlet chamber 72 extends below the intersection of the walls of the bore 62 and the piston 50.

At the end of the bore 62 opposite the piston 50, a second check valve assembly 74 is provided. The second check valve assembly 74 includes a ball 75 and a seat 76. Preferably, the second check valve assembly 74 is formed of a material that is sufficient to sustain operation of the pump assembly 60 under operating conditions within the pump assembly 60 as described herein, such as the relatively high operating pressures of a pump assembly within a vehicle brake system. Additionally, in a preferred embodiment, second check valve assembly 74 is comprised of materials that are compatible with hydraulic brake fluid. A pumping chamber 77 is defined within the bore 62 between the second check valve assembly 74 and the combination of the piston 50 and the seal 63. As is evident from the structure of the pump 60 and as will be evident from the operation of the pump 60 described below, the pump 60 is highly efficient due to the relatively small unswept volume of the piston 50.

The operation of the pump assembly 60 will now be described. At the end of a pumping stroke, when the piston 50 is closest to the second check valve assembly 74, the seal 63 is in the second position, thereby seated against the sealing surface 69 of the inlet flange 53 (the first check valve assembly 70 is shut). During a fluid inlet stroke, the piston 50 moves away from the second check valve assembly 74. The seal 63 is disposed between the retaining flange 52 and the inlet flange 53, and, as the piston 50 moves away from the second check valve assembly 74, pressure in the pumping chamber 77 drops below the pressure in the inlet chamber 72 as the pumping chamber 77 expands. The differential pressure unseats the seal 63 from the inlet flange 53, opening the first check valve assembly 70 and allowing fluid to flow from the inlet chamber 72 through the passageways 59, 57, and 58, into the pumping chamber 77. The seal 63 will generally have greater friction to the wall of the bore 62 than to the piston 50, and will tend to remain stationary as the piston 50 moves. However, as the piston 50 continues to move away from the second check valve assembly 74, the retaining flange 52 will eventually intercept the seal 63, and the seal 63 will be drug away from the second check valve assembly 74 by the retaining flange 52 of the piston 50, so that the seal 63 is now in the first position thereof. Once the seal 63 has been intercepted by the retaining flange 52, the seal 63 will remain seated against the retaining flange 52 as long as the piston 50 continues to move in the same direction, e.g., away from the second check valve assembly 74.

During a pumping stroke, the piston 50 moves back toward the second check valve assembly 74. As the piston 50 moves, the seal 63 again tends to remain stationary due to friction with the wall of the bore. Additionally, as the pumping chamber gets smaller as the piston 50 moves toward the second check valve assembly 74, pressure starts to rise, even with the first check valve assembly 70 still open, due to head losses in the passageways. Thus, the seal 63 moves out of the second position thereof. As the piston 50 continues to move toward the second check valve assembly 74, the inlet flange 53 will eventually intercept the seal 63, and the seal 63 will be drug toward the second check valve assembly 74 by the inlet flange 53 of the piston 50. Once the seal 63 has been intercepted by the inlet flange 53, the seal 63 will remain in the second position thereof, i.e. seated against the inlet flange 53, as long as the piston 50 continues to move in the same direction, e.g., toward the second check valve assembly 74. When the seal 63 is in the second position thereof, the first check valve assembly 70 is in the closed position, as illustrated in FIG. 5. With the seal 63 seated against the sealing surface 69 of the inlet flange 53, fluid cannot flow into the at least one passageway 59 from the at least one passageway 57. Therefore, the pumping chamber 77 is isolated from the inlet chamber 72. Thus, as the piston 50 moves further into the bore 62, the volume of the pumping chamber 77 decreases, and pressure is raised in the fluid within the pumping chamber 77.

As the piston 50 continues to move toward the second check valve assembly 74, the fluid pressure within the chamber 77 continues to build until the fluid pressure within the chamber 77 is greater than the resistance required to unseat the ball 75 from the seat 76 of the second check valve assembly 74. When the ball 75 is unseated, the second check valve assembly 74 opens and pressurized fluid is discharged from the pump 60 via an outlet 78.

As the piston 50 continues to move toward the second check valve assembly 74, the volume of the inlet chamber 72 increases. The increase in volume of the inlet chamber 72 may create negative pressure or a vacuum pressure within the inlet chamber 72. This vacuum pressure within the inlet chamber 72 pulls fluid from the fluid inlet 73 into the inlet chamber 72. Thus, the pump assembly 60 may be a self-priming or pre-charging pump, and the pump assembly 60 may operate with negative pressure conditions within the inlet chamber 72. At the end of a pumping stroke, the first end portion 54 of the piston 50 is relatively close to the second check valve assembly 74. With the piston 50 in this position, the first check valve assembly 70 and the second check valve assembly 74 are in relatively close proximity to one another, such that the pumping chamber 77 is relatively small, as compared to the pumping chambers of conventional pumps. The axial distance between the first check valve assembly 70 and the second check valve assembly 74 is minimized so that the pump assembly 60 has a relatively small unswept volume.

It will be appreciated that the size and design of the seal 63, the at least one passageway 58 of the retaining flange 52, and the at least one passageway 59 of the inlet flange 53, must be coordinated so that the seal 63 and piston 50 cooperate such that the pump 60 operates as described above. Conversely, it will be appreciated that the seal 63, the at least one passageway 58 of the retaining flange 52, and the at least one passageway 59 of the inlet flange 53 could be any size or shape capable of performing as described above.

Referring now to FIG. 6, there is illustrated a portion of a second embodiment of a pump assembly, indicated generally at 160, in accordance with this invention. The pump assembly 160 is similar to the pump assembly 60, and only those elements that differ will be described herein, and corresponding elements have been given the same reference numeral incremented by 100.

The piston 150 includes a retaining flange 152, an inlet flange 153, and an intermediate portion 155 disposed therebetween. Unlike the intermediate portion 55 of the piston 50, the intermediate portion 155 of the piston 150 does not have a passageway formed therethrough. Instead, the intermediate portion 155 is preferably circular in cross-section, and is slidingly engaged by a seal 163. The seal 163 may reciprocate between the retaining flange 152 and the inlet flange 153, in a manner similar to that described above for the seal 63.

The seal 163 differs from the seal 63 in that the seal 163 has at least one passageway 180 formed therethrough. The at least one passageway 180 has an outer radius R₁ from the axis A. The outer radius R1 is smaller than the inner radius R₄ of the at least one passageway 159 in the inlet flange 153. The outer radius R₁ is larger than the inner radius R₃ of the at least one passageway 158 in the retaining flange 152.

The seal 163 and the inlet flange 153 form a check valve assembly 170. However, the structure of the check valve assembly 170 varies from structure of the check valve assembly 70. The at least one passageway 158 in the retaining flange 152 is communicably connected to the at least one passageway 180 in the seal 163. In a preferred embodiment, the at least one passageway 180 is a plurality of passageways sized such that no matter how the seal 163 is rotated relative to the retaining flange 152, the at least one passageway 180 is communicably connected to the at least one passageway 158 of the retaining flange 152, when the seal 163 is seated against the surface 168.

When the seal 163 is in a first position relative to the inlet flange 153, the seal 163 is unseated from the sealing surface 169 of the inlet flange 153, and may be seated against the surface 168 of the retaining flange 152, as described in the previous embodiment and as shown in FIG. 6. When the seal 163 is in the first position, fluid is allowed to flow through the at least one passageway 159, below the seal 163, through the passageway 180, through the at least one passageway 158, and into the pumping chamber 177. Thus, the check valve assembly 170 is in a flow-through position. When the seal 163 is in a second position, seated against the sealing surface 169 of the inlet flange 153, the at least one passageway 180 in the seal 163 is prevented from communicating with the at least one passageway 159. Thus, the check valve assembly 170 is in a closed position, such that the pump 160 works in a manner similar to that described for the pump 60.

The pistons 50, 150, seals 63, 163 and pump assemblies, 60, 160 have been described for use in a vehicle braking system, including, but not limited to, vehicle braking systems having anti-lock braking systems, and/or integrated or stand alone traction control and vehicle stability control systems. However, it will be appreciated that the pistons 50, 150, the seals 63, 163 and pump assemblies 60, 160 may be used in any vehicle component or in any other device requiring a piston, seal, or pump assembly.

Referring to FIGS. 7 and 8, and using like reference numbers to indicate corresponding parts, there is illustrated a third embodiment of a pump assembly, indicated generally at 300. As shown therein, the pump assembly 300 includes the housing 61 having the longitudinal bore 62 (axial in the illustrated embodiment) formed therethrough. Fluid may be supplied to the bore 62 of the pump assembly 300 through the fluid inlet 73. The second check valve assembly 74 is disposed in an outlet end 62A of the bore 62 (upper end as viewed in FIGS. 7 and 8) and includes the fluid outlet 78 having the seat 76 formed therein for receiving the ball 75.

A piston 302 is mounted for reciprocal movement within the bore 62 of the housing 61. The piston 302 includes a shaft or piston body 304 having a first end 304A and a second end 304B. The piston body 304 includes an inlet flange 306 extending radially outwardly from the piston body 304. The illustrated retaining flange 308 extends radially outwardly from the piston body 304 and has a substantially square transverse section, as best shown in FIG. 10. It will be understood that the transverse section of the retraining flange 308 may have any other polygonal shape. In the illustrated embodiment, the portion of the retaining flange 308 extending outwardly of the piston body 304 is shaped substantially as a right square prism. An intermediate portion 310 is defined between the inlet flange 306 and the retaining flange 308.

In the illustrated embodiment, an outer peripheral surface 312 of the inlet flange 306 and the outer peripheral surface 314 of the intermediate portion 310 are substantially cylindrical in shape. It will be understood, however, that the outer peripheral surfaces 312 and 314 of the inlet flange 306 and the intermediate portion 310, respectively, may have any other desired shape, such as a polygonal transverse section. The illustrated piston 302 includes an annular seal 316 disposed around the intermediate portion 310.

The illustrated piston body 304 includes a first body portion 318 between the first end 304A and the retaining flange 308. As best shown in FIG. 9, an outer circumferential surface 320 of the first body portion 318 includes a plurality of radially arrayed flat portions 322 extending axially from the retaining flange 308 toward the first end 304A of the piston body 304. In the illustrated embodiment, each of the four illustrated flat portions 322 is substantially coplanar with a peripheral side surface 324 of the retaining flange 308. The illustrated flat portions 322 and the wall of the bore 62 define a portion of the second passageway 326 (described in detail below). It will be understood that any desired number of flat portions 322 may be formed on the first body portion 318, such as one flat portion 322 and two or more flat portions 322.

The illustrated piston body 304 further includes a second body portion 328 between the second end 304B and the inlet flange 306. The illustrated second body portion 328 includes a reduced diameter portion 330. If desired, a sealing member, such as an O-ring (not shown) may be disposed about the reduced diameter portion 330. It will be understood however, that the second body portion 328 may be formed having a uniform diameter or having more than two diameters.

As best shown in FIGS. 7 and 8, the outer peripheral surface 312 of the inlet flange 306 and the wall of the bore 62 define a first passageway 332. Similarly, the peripheral side surfaces 324 of the retaining flange 308 and the wall of the bore 62 define a second passageway 326. An outer peripheral surface 317 of the seal 316 slidingly engages the wall of the bore 62 and cooperates with the piston 302 to define the first check valve assembly 334. The illustrated bore 62 is divided into the inlet chamber 72 and the pumping chamber 77 by the first check valve assembly 334.

During operation of the pump assembly 300, the piston is reciprocated between the first position (toward one extreme of piston 302 travel, as shown in FIG. 7) and the second position (toward another extreme of piston 302 travel, as shown in FIG. 8) as described in detail herein above. As the piston 302 moves from the first position (see FIG. 8) to the second position (see FIG. 7), the seal 316 sealingly engages the inlet flange 306, thereby moving the first check valve assembly 334 to the closed position, as best shown in FIG. 7.

As described in detail herein above, as the piston 302 continues to move toward the second check valve assembly 74, the fluid pressure within the pumping chamber 77 increases until the fluid pressure within the pumping chamber 77 is greater than the force required to unseat the ball 75 from the seat 76 of the second check valve assembly 74, and allow pressurized fluid (represented by the arrow 336) to discharge from the pump assembly 300 through the outlet 78.

As the piston 302 moves from the second position (FIG. 8) to the first position (FIG. 7), the seal 316 moves away from the inlet flange 306 toward the retaining flange 308, thereby moving the first check valve assembly 334 to the open position or flow-through position to allow fluid (represented by the arrow 338) to fill the pumping chamber 77, as best shown in FIG. 8. In the open position, fluid is caused to flow through the first and second passageways 332 and 326, respectively, and between the intermediate portion 310 and an inner surface 315 of the seal 316.

Referring to FIG. 11, and using like reference numbers to indicate corresponding parts, there is illustrated a fourth embodiment of a piston, indicated generally at 402. The illustrated piston 402 includes a first body portion 418 between the first end 404A and the retaining flange 308. As best shown in FIG. 11, the first body portion 418 has the shape of the frustum of a cone. An outer circumferential surface 420 of the first body portion 418 includes a plurality of radially arrayed flat portions 422. The flat portions 422 include a first planar area 422A extending axially from the retaining flange 308 toward the first end 404A and a second planar area 422B extending axially from the first planar area 422A into the intermediate portion 310. In the illustrated embodiment, each of the flat portions 422 is substantially coplanar with a peripheral side surface 324 of the retaining flange 308. A peripheral edge of the first planar areas 422A defines a hyperbola. The illustrated flat portions 422 and the wall of the bore 62 (such as illustrated in FIGS. 7 and 8) define a portion of the second passageway 326, described in detail above.

Referring to FIG. 12, and using like reference numbers to indicate corresponding parts, there is illustrated a fifth embodiment of a piston, indicated generally at 502. The illustrated piston 502 includes a first body portion 518 between the first end 504A and the retaining flange 308. The illustrated first body portion 518 includes a first part 518A having the shape of the frustum of a cone, and a second part 518B having the shape of a cylinder. An outer circumferential surface 520 of the first body portion 518 includes a plurality of radially arrayed flat portions 522 extending axially from the retaining flange 308 toward the first end 504A.

The illustrated flat portions 522 include a first planar area 522A in the first part 518A coplanar with a second planar area 522B in the second part 518B, and further coplanar with a third planar area 522C in the intermediate portion 310. In the illustrated embodiment, the second planar area 522B extends axially from the retaining flange 308 toward the first end 504A, and the first planar area 522A extends axially from the second planar area 522B toward the first end 504A. The third planar area 522C extends axially from the second planar area 522B into the intermediate portion 310. In the illustrated embodiment, each of the planar areas 522A, 522B, 522C of the flat portions 522 is substantially coplanar with a peripheral side surface 324 of the retaining flange 308. A peripheral edge of the first planar area 522A defines a hyperbola, and the peripheral edges of the second planar area 522B and the third planar area 522C each define a rectangle. The illustrated flat portions 522 and the wall of the bore 62 (such as illustrated in FIGS. 7 and 8) define a portion of the second passageway 326, described in detail above.

The principle and mode of operation of the pump assembly have been described in its various embodiments. However, it should be noted that the pump assembly described herein may be practiced otherwise than as specifically illustrated and described without departing from its scope. 

1. A pump apparatus comprising: a housing having a bore formed therethrough; a piston disposed within said bore for reciprocal movement therein, said piston comprising: a piston body; an inlet flange extending radially outwardly from said piston body, an outer peripheral surface of said inlet flange and a wall of said bore defining a first passageway; a retaining flange extending radially outwardly from said piston body and having a substantially square transverse section, an outer peripheral surface of said retaining flange and said wall of said bore defining a second passageway; and an intermediate portion disposed between said inlet flange and said retaining flange; an annular seal disposed around said intermediate portion of said piston body, said seal slidingly engaging said wall of said bore, said seal and said piston cooperating to form a check valve assembly.
 2. The pump apparatus of claim 1, wherein said bore of said housing is divided into an inlet chamber and a pumping chamber by said check valve assembly, said seal being moveable to a first position spaced apart from said inlet flange such that said check valve assembly is in a flow-through position to allow fluid to fill the pumping chamber, such that fluid flows between said seal and said intermediate portion of said piston, said seal being further moveable to a second position sealing against said inlet flange such that said check valve assembly is in a closed position to allow fluid within said pumping chamber to be pressurized during movement of said piston in a pumping stroke.
 3. The pump apparatus of claim 1, wherein an outer peripheral surface of said intermediate portion is substantially cylindrical.
 4. The pump apparatus of claim 1, wherein an outer peripheral surface of said inlet flange is substantially cylindrical.
 5. The pump apparatus of claim 2, wherein said piston body includes: a first end extending into said pumping chamber; a second end extending into said inlet chamber; a first body portion between said first end and said retaining flange, an outer circumferential surface of said first body portion including a flat portion extending axially from said retaining flange toward said first end of said piston body, said flat portion being substantially coplanar with a peripheral side surface of said retaining flange; and a second body portion between said second end and said inlet flange.
 6. The pump apparatus of claim 5, wherein said first body portion includes four radially arrayed flat portions extending axially from said retaining flange toward said first end of said piston body, each of said flat portions being substantially coplanar with a peripheral side surface of said retaining flange.
 7. The pump apparatus of claim 5, wherein said flat portion and said wall of said bore define a portion of said second passageway.
 8. The pump apparatus of claim 5, wherein said second body portion includes a reduced diameter portion.
 9. A check valve assembly for a vehicle braking system pump comprising: a piston including: a piston body; an inlet flange extending radially outwardly from said piston body; a retaining flange extending radially outwardly from said piston body and having a substantially square transverse section; and an intermediate portion disposed between said inlet flange and said retaining flange; and an annular seal disposed around said intermediate portion of said piston, said seal and said piston cooperating to form a check valve assembly, said seal being moveable to a first position spaced apart from said inlet flange such that said check valve assembly is in a flow-through position, wherein a passageway is defined between said seal and said intermediate portion of said piston, said seal being moveable to a second position sealing against said inlet flange in which said check valve assembly is in a closed position.
 10. The check valve assembly of claim 9, wherein an outer peripheral surface of said intermediate portion is substantially cylindrical.
 11. The check valve assembly of claim 9, wherein an outer peripheral surface of said inlet flange is substantially cylindrical.
 12. The check valve assembly of claim 9, wherein said piston body further includes: a first end; a second end; a first body portion between said first end and said retaining flange, an outer circumferential surface of said first body portion including a flat portion extending axially from said retaining flange toward said first end of said piston body, said flat portion being substantially coplanar with a portion of a peripheral side surface of said retaining flange; and a second body portion between said second end and said inlet flange.
 13. The check valve assembly of claim 12, wherein said first body portion includes a plurality of radially arrayed flat portions extending axially from said retaining flange toward said first end of said piston body, each of said flat portions being substantially coplanar with a portion of a peripheral side surface of said retaining flange.
 14. The check valve assembly of claim 12, wherein said flat portion defines a fluid flow path.
 15. The check valve assembly of claim 12, wherein said second body portion a includes a reduced diameter portion.
 16. A piston and seal assembly for a vehicle braking system pump comprising: a piston having a first end, a second end, an inlet flange, a retaining flange, and an intermediate portion disposed between said inlet flange and said retaining flange, a first piston portion being defined between said retaining flange and said first end of said piston, and a second piston portion being defined between said inlet flange and said second end of said piston; and an annular seal disposed around said intermediate portion of said piston, said seal and said piston cooperating to form a first check valve assembly, said seal being moveable to a first position relative to said inlet flange in which said first check valve assembly is in a flow-through position, wherein a passageway is defined between said seal and said intermediate portion of said piston, said seal being moveable to a second position relative to said inlet flange in which said first check valve assembly is in a closed position; wherein an outer circumferential surface of said first piston portion includes at least one flat portion extending axially from said retaining flange toward said first end of said piston, said at least one flat portion defining a plane parallel with an axis of said piston.
 17. The piston and seal assembly of claim 16, wherein said first piston portion has the shape of the frustum of a cone, a peripheral edge of said at least one flat portion defining a hyperbola.
 18. The piston and seal assembly of claim 16, wherein said first piston portion includes a first part and a second part, said first part having the shape of the frustum of a cone, said second part having the shape of a cylinder and being between said retaining flange and said first part, and wherein said at least one flat portion includes a first planar area in said first part coplanar with a second planar area in said second part, said first planar area having a peripheral edge defining a hyperbola, said second planar area having a peripheral edge defining a rectangle.
 19. The piston and seal assembly of claim 18, wherein said at least one flat portion further includes a third planar area in said intermediate portion and coplanar with said first and second planar areas, said third planar area having a peripheral edge defining a rectangle. 